CASINO manual - Theory of Condensed Matter

where σ is the spin index of the particle, i is the index of the particle within its spin channel
and (x, y, z) is the position of the particle.
INPUT EXAMPLE (Logical) If input example is T then an example of a casino input file with
all currently known keywords and their default values will be written out. A modified version
of this can be used as an input file in future runs.
INT SF (Logical) If int sf is set to T then the electron–electron interaction energy for a periodic
system will be calculated in terms of the structure factor. The structure factor should either
have been accumulated in a previous run and stored in an available expval.data file, or its
accumulation should be flagged for the current run. Using this method the total interaction
energy can be separated into Hartree and XC terms. This feature is not currently documented
in the manual.
HARTREE XC (Logical) Flag the computation of separate Hartree and exchange-correlation (XC)
parts of the electron-electron interaction energy for a periodic system. This may be done in two
different ways, namely the structure factor method and the MPC method. The computation
thus requires either (1) structure factor information from a previously accumulated expval.data
file or from setting structure factor=T, or (2) the MPC interaction to be active (through
interaction=mpc, mpc ewald or ewald mpc). If both these things are true then both methods
will be used to compute the hartree/XC energies (the resulting numbers should agree reasonably
closely). If neither are true, then this keyword has no effect. The default is T. Note that the
MPC version only works with 3D periodicity.
INTERACTION (Integer) Type of interaction between particles. interaction can take the following
values:
‘none’: noninteracting particles;
‘coulomb’: Coulomb interaction;
‘ewald’: periodic Coulomb interaction computed using Ewald summation;
‘mpc’: periodic Coulomb interaction computed using the MPC method;
‘ewald mpc’: compute and report both Ewald and MPC results, but use Ewald in DMC propagation;
‘mpc ewald’: compute and report both Ewald and MPC results, but use MPC in DMC propagation;
‘manual’: compute a user-defined interaction (see the manual interaction block input keyword);
The values ‘coulomb’ and ‘ewald’ can be used interchangeably, although ‘coulomb’ should strictly
refer to aperiodic systems and ‘ewald’ to periodic systems.
The MPC interaction is generally significantly faster than the Ewald interaction and should give
smaller finite-size effects. The MPC interaction is not currently implemented for 1D systems,
however. Furthermore, we recommend using ‘ewald mpc’ rather than ‘mpc’ or ‘mpc ewald’, as
there is some evidence that the MPC interaction can distort the XC hole. See Sec. 19.4 for
information about the Ewald interaction, Sec. 19.4.4 for information about the MPC and Sec.
20 for information about ‘manual’ interactions.
ISOTOPE MASS (Real) This keyword can be used to define a nuclear mass (in amu) if you need
to override the default value used in casino (which is averaged over isotopes according to their
abundances). The default (given in the table in Sec. 32) is used if isotope mass is set to zero.
The atomic mass unit (amu) in this sense means ‘the ratio of the average mass per atom of the
element to 1/12 of the mass of 12 C’. This is only relevant if relativistic is set to T. See Sec. 32.
JASBUF (Logical) If jasbuf is T then the one-body (χ and q) terms in the Jastrow factor for each
electron in each configuration are buffered in DMC: this saves time at the expense of memory.
Clearly this will have no effect in systems without one-body terms in the Jastrow factor.
JASTROW PLOT (Block) This utility allows the user to plot the u(r ij ), χ(r i ), f(r i , r j , r ij ), p(r ij )
and q(r i ) terms in the Jastrow factor. The first line is a flag specifying whether the Jastrow
factor is to be plotted (0=NO, 1=YES); the second line holds the spin of particle i = 1, 2, . . .; the
third line holds the spin of particle j = 1, 2, . . .. Optionally, another three lines may be given: the
fourth line holds the (x, y, z)-position of particle j; the fifth line holds a vector with the direction
in which i is moved; and the sixth line holds the position vector of a point on the straight line
along which electron i moves. If lines 4–6 are not given, default values will be inserted. The
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